Browsing by Author "Andrews, Sean"

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    A Dust-trapping Ring in the Planet-hosting Disk of Elias 2-24
    (2024) Carvalho, Adolfo S.; Perez, Laura M.; Sierra, Anibal; Mellado, Maria Jesus; Hillenbrand, Lynne A.; Andrews, Sean; Benisty, Myriam; Birnstiel, Tilman; Carpenter, John M.; Guzman, Viviana V.; Huang, Jane; Isella, Andrea; Kurtovic, Nicolas; Ricci, Luca; Wilner, David J.
    Rings and gaps are among the most widely observed forms of substructure in protoplanetary disks. A gap-ring pair may be formed when a planet carves a gap in the disk, which produces a local pressure maximum following the gap that traps inwardly drifting dust grains and appears as a bright ring owing to the enhanced dust density. A dust-trapping ring would provide a promising environment for solid growth and possibly planetesimal production via the streaming instability. We present evidence of dust trapping in the bright ring of the planet-hosting disk Elias 2-24, from the analysis of 1.3 and 3 mm Atacama Large Millimeter/submillimeter Array observations at high spatial resolution (0.'' 029, 4.0 au). We leverage the high spatial resolution to demonstrate that larger grains are more efficiently trapped and place constraints on the local turbulence (8 x 10(-4) < alpha( turb) < 0.03) and the gas-to-dust ratio (Sigma (g) /Sigma (d) < 30) in the ring. Using a scattering-included marginal probability analysis, we measure a total dust disk mass of M-dust=13.8(-0.5)+0.7x10(-4)M(circle dot) . We also show that at the orbital radius of the proposed perturber the gap is cleared of material down to a flux contrast of 10(-3) of the peak flux in the disk.
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    Constraints on the Physical Origin of Large Cavities in Transition Disks from Multiwavelength Dust Continuum Emission
    (2024) Sierra, Anibal; Perez, Laura M.; Sotomayor, Benjamin; Benisty, Myriam; Chandler, Claire J.; Andrews, Sean; Carpenter, John; Henning, Thomas; Testi, Leonardo; Ricci, Luca; Wilner, David
    The physical origin of the large cavities observed in transition disks is to date still unclear. Different physical mechanisms (e.g., a companion, dead zones, enhanced grain growth) produce disk cavities of different depth, and the expected spatial distribution of gas and solids in each mechanism is not the same. In this work, we analyze the multiwavelength interferometric visibilities of dust continuum observations obtained with Atacama Large Millimeter/submillimeter Array and Very Large Array for six transition disks: CQTau, UXTau A, LkCa15, RXJ1615, SR24S, and DMTau, and calculate brightness radial profiles, where diverse emission morphology is revealed at different wavelengths. The multiwavelength data are used to model the spectral energy distribution and compute constraints on the radial profile of the dust surface density, maximum grain size, and dust temperature in each disk. They are compared with the observational signatures expected from various physical mechanisms responsible for disk cavities. The observational signatures suggest that the cavities observed in the disks around UXTau A, LkCa15, and RXJ1615 could potentially originate from a dust trap created by a companion. Conversely, in the disks around CQTau, SR24S, DMTau, the origin of the cavity remains unclear, although it is compatible with a pressure bump and grain growth within the cavity.
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    Exploring the Complex Ionization Environment of the Turbulent DM Tau Disk
    (2024) Long, Deryl E.; Cleeves, L. Ilsedore; Adams, Fred C.; Andrews, Sean; Bergin, Edwin A.; Guzman, Viviana V.; Huang, Jane; Hughes, A. Meredith; Qi, Chunhua; Schwarz, Kamber; Simon, Jacob B.; Wilner, David
    Ionization drives important chemical and dynamical processes within protoplanetary disks, including the formation of organics and water in the cold midplane and the transportation of material via accretion and magnetohydrodynamic flows. Understanding these ionization-driven processes is crucial for understanding disk evolution and planet formation. We use new and archival Atacama Large Millimeter/submillimeter Array observations of HCO+, H13CO+, and N2H+ to produce the first forward-modeled 2D ionization constraints for the DM Tau protoplanetary disk. We include ionization from multiple sources and explore the disk chemistry under a range of ionizing conditions. Abundances from our 2D chemical models are postprocessed using non-LTE radiative transfer, visibility sampling, and imaging, and are compared directly to the observed radial emission profiles. The observations are best fit by a modestly reduced cosmic-ray ionization rate (zeta CR similar to 10-18 s-1) and a hard X-ray spectrum (hardness ratio = 0.3), which we associate with stellar flaring conditions. Our best-fit model underproduces emission in the inner disk, suggesting that there may be an additional mechanism enhancing ionization in DM Tau's inner disk. Overall, our findings highlight the complexity of ionization in protoplanetary disks and the need for high-resolution multiline studies.